91影视

$SSS$- Side 鈥� Side 鈥� Side method means if three sides of one triangle are equal to three sides of another triangle, then the triangles are congruent.

$SAS$ 鈥� Side 鈥� Angle 鈥� side method means if two sides and the included angle of one triangle are equal to the corresponding sides and angle of another triangle, then triangles are congruent.

$ASA$- Angle 鈥� side 鈥� angle method means if two angles and the included side of one triangle are equal to the corresponding angles and side of another triangle, then triangles are congruent.

$AAS$鈥� Angle 鈥� angle 鈥� side method if two angles and the non-included side of one triangle are equal to the corresponding angles and side of another triangle, then triangles are congruent.

$HL$鈥� Hypotenuse 鈥� leg method means if the hypotenuse and one leg of one right-angled triangle are equal to the corresponding hypotenuse and leg of another right-angled triangle, then two triangles are congruent.

In the figure, $\stackrel{炉}{AO}鈯�\text{辫濒补苍别鈥�}M$and also $\stackrel{炉}{AB}鈮�\stackrel{炉}{AC}$.

In order to prove the congruency of triangles$螖\text{AOB}$and$螖\text{AOC}$of which sides, $BO$and $OC$lies on plane $M$ observe the following:

i. (Right - Angle) -Since,$\stackrel{鈫�}{\text{AO}}鈯�$ plane M, so,$\text{AO}鈯�\text{BO}$ and $\text{AO}鈯�\text{OC}$, which implies that $鈭�\text{AOB}鈮�鈭�\text{AOC}$.It is given that,$\text{BO}鈮�\text{CO}$.

ii. (Hypotenuse) - It is given that $AB鈮�AC$.

iii. (Leg) - Side $\text{AO}=\text{OA}$is common in both triangles.

Therefore, by $HL$congruency method $螖\text{AOB}鈮�螖\text{AOC}$.